**Date:** Fri, 30 Sep 2005 21:37:52 +0100
**Reply-To:** Josh Johnson <joshjohnson88990@yahoo.co.uk>
**Sender:** "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
**From:** Josh Johnson <joshjohnson88990@yahoo.co.uk>
**Subject:** Stability estimation: test-retest alpha reliability coefficient
**Content-Type:** text/plain; charset=iso-8859-1
Hi all,

A question regarding test-retest reliability/stability calculation-

For the simple case of, for example, n respondents measured twice each (say, a month apart between administrations) on only one test/question. The calculation of the coefficient alpha seems to me straight forward in SPSS-

àSelect the two variables (the test and retest) to the variable box, àselect alpha, two way mixed (consistency) as the model.

(This is assuming the n respondents are a random sample of the larger population but the one question/test is the only item we are interested in and not a sample of a larger group of questions)

However how does one calculate the coefficient alpha when more then one measurement/question is asked for each respondent? For example a case where 20 questions are asked twice (test-retest)- is there an overall alpha I can calculate or am I confined to calculating separate alpha’s for each question? Assuming again that the respondents are a random sample and the 20 questions are fixed (not a sample of a larger group of questions I am interested in asking)

Any advice, references will be greatly appreciated.

Thanks in advance,

Josh

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